Datasheet
DocID14117 Rev 4 35/44
B5973D Application information
44
Figure 22. Positive buck-boost regulator
8.7 Negative buck-boost regulator
In Figure 23, the schematic circuit for a standard buck-boost topology is shown. The output
voltage is:
Equation 37
where the ideal duty cycle D for the buck boost converter is:
Equation 38
The considerations given in Section 8.6 for the real duty cycle are still valid here.
Also Equation 34 till Equation 36 can be used to calculate the maximum output current.
So, as an example, considering the conversion V
IN
= 12 V to V
OUT
= -5 V, I
LOAD
= 0.5 A:
Equation 39
Equation 40
An important thing to take into account is that the ground pin of the device is connected to
the negative output voltage. Therefore, the device is subjected to a voltage equal to
V
IN
- V
O
, which must be lower than 36 V (the maximum operating input voltage).
95()
9&&
6<1&
&203
287
)%
,1+
*1'
%'
9,1 9
9287 9 $
&
)
9
&(5$0,&
&
Q)
5
&
S)
5
5
/ +
'
6736/
&
)
9
(65 ! P
'
6736/
0
6711)/
$0
V
OUT
V
IN
–
D
1D–
-------------=
D
V–
OUT
V
IN
V
OUT
–
------------------------------=
D
5
512+
---------------- 0.706==
I
SW
I
LOAD
1D–
---------------
0.5
10.706–
------------------------ 1.7A== =